High severity reforming process with a platinum-iridium catalyst

ABSTRACT

Naphtha feed stocks are converted to high octane products in a long cycle semi-regenerative operation utilizing a catalyst comprising alumina in association with 0.15 to 0.75 weight percent platinum, 0.15 to 0.45 weight percent iridium and 0.3 to 2.0 weight percent chlorine, each based on total catalyst, the surface area of the platinum and iridium on the alumina being at least about 200 square meters per gram of platinum and iridium as determined by carbon monoxide chemisorption techniques. The catalyst should contain less than about two atoms of sulfur per atom of platinum and iridium and be substantially free of alkali and alkaline earth metal constituents.

United States Patent 1191 Sinfelt et a1.

1 Oct. 1, 1974 HIGH SEVERITY REFORMING PROCESS WITH A PLATINUM-IRIDIUMCATALYST [73] Assignee: Esso Research and Engineering Company, Linden,NJ.

[22] Filed: Apr. 12, 1973 [21] Appl. No.2 350,403

Related US. Application Data [63] Continuation-impart of Ser. No.194,461, Nov. 1, 1971, which is a continuation-in-part of Ser. No.883,601, Dec. 9, 1969, abandoned.

[52] US. Cl. 208/139, 252/441 [51] Int. Cl Cl0g 35/06, BOlj 11/78 [58]Field of Search 208/139 [56] References Cited UNlTED STATES PATENTS2,848,377 8/1958 Webb 208/138 40o Invention CYCLE LENGTH, MONTHS2,911,357 11/1959 Myers et a1. 208/138 3,487,009 12/1969 Jacobson et al.208/138 Primary Examiner-Delbert E. Gantz Assistant Examiner-S. BergerAttorney, Agent, or Firm.lay Simon 1 5 7 ABSTRACT Naphtha feed stocksare converted to high octane products in a long cycle semi-regenerativeoperation utilizing a catalyst comprising alumina in association with0.15 to 0.75 weight percent platinum, 0.15 to 0.45 weight percentiridium and 0.3 to 2.0 weight percent chlorine, each based on totalcatalyst, the surface area of the platinum and iridium on the aluminabeing at least about 200 square meters per gram of platinum and iridiumas determined by carbon monoxide chemisorption techniques. The catalystshould contain less than about two atoms of sulfur per atom of platinumand iridium and be substantially free of alkali and alkaline earth metalconstituents.

8 Claims, 1 Drawing Figure SEVERITY FACTOR CYCLE LENGTH, MONTHSPAIENTEDUBI H974 invention 0.3 P1 0.3 Re

SEVERITY' FACTOR HIGH SEVERITY REFORMING nkocnss WIT A PLATlNUM -IRIDIUMCATALYST CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of Ser. No. 194,461, filed Nov. 1, 1.971 which, inturn, is a continuation-in-part of Ser. No. 883,601, filed Dec. 9, 1969,now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention 1 This inventionrelates to a naphtha reforming process utilizing a supportedplatinum/iridium catalyst that is conducted for long oft-stream periods.More particularly, the present invention relates to the use of analumina supported platinum/iridium/chlorine catalyst in a naphthahydroforming operation conducted for long on-stream periods i I 2.Description of the Prior Art I The use of iridium-containing catalystsin naphtha reforming operations has been reported in the patentliterature. Webb et al., in US. Pat. No. 2,848,377, disclose thatsupported iridium/platinum metal combinations are effective hydrocarbonconversion catalysts. Sinfelt et al., in US. PatINo. 3,567,625, teachthat combinations or iridium with Group I13 metals are effectivehydroforming catalysts. Kob erstein, in German patent 1,108,361, teachesthat supported platinum catalysts containing minor amounts of iridiumcan be employed to reform heavy petroleum fractions. Further, thepatentees of US. PatjNosI 3,487,009; 3,507,780; 3,507,781; 3,554,902 and3,578,583 disclose the existence of various types of supportediridium-containing catalysts and their use in the hydroforming ofnaphtha fractions.

SUMMARY OF THE INVENTION Pursuant to the present invention, it has beendiscovered that specific types of alumina supported'platinum-/iridium/chlorine-containing catalysts can'be employed in naphthareforming operations to produce high oc tane C reformate product forprotracted on-stream periods without significant yield losses during thecourse of the reforming'operation. In particular, it has been discoveredthat alumina supported platinum/iridium/chlorine catalysts can besuccessfully employed in naphtha hydroforming operations for on streamcycles beyond those obtainable with commercially available reformingcatalysts at identical process conditions.

BRIEF DESCRIPTION OF DRAWING The FIGURE illustrates the relationshipbetween severity factor (as hereinafter defined) and the cycle lengthobtainable in a semi-regenerative reforming operation whereinplatinum/iridiumcatalysts and commercially available platinum/rheniumand platinum catalysts are used to reform a naphtha feed stock having aWatson characterization factor or from 11.4 to 12.2 at a temperatureranging from about 750 to 1,050F and a pressure varying from about 150to 600 psig. In general, the lower operating line of each bandrepresents the performance level obtainable with a difficultlyreformable feed and the upper operating line represents the performancelevel obtainable with an easily reformable feed. 8

The reforming of petroleum naphtha to products having increased octanenumbers utilizing noble metal type catalysts is a well known refineryprocess. Basically, there are two types of reforming units, namely,semi-regenerative type units wherein the unit is onstream for two ormore months between catalyst regenerations and cyclic units wherein thecatalyst is regenerated more frequently. The present invention isconcerned with a reforming process carried out in the semi-regenerativemode.'ln a typical semi-regenerative process, the catalyst is maintainedas a fixed bed within a number of serially connected, adiabaticallyoperated reactors. The naphtha feed stock, preferably a substantiallysulfur-free naphtha feed stock, is mixed with hydrogen, generallycontained in a recycle gas, and heated in a preheat furnace and/orbyindirect heat exchange with a product stream and introduced to thefirst reactor of the reactor train. The effluent from the first reactoris passed through a reheat furnace and introduced to the second reactorin the train. This sequence is repeated as the process effluent istreated in subsequent reactors. The temperature to which the feed andhydrogen are heated depends on the condition of the catalyst within theindividual reaction zones. With a fresh or freshly regenerated catalyst,the inlet temperature to each reaction zone may be as low as 875F.During the course of the reforming reaction, carbonaceous residuesdeposit on the catalyst and the catalyst activity diminishes. Thisdeactivation requires that the feed stock and hydrogen be heated to ahigher inlet temperature to maintain the same product octane level. Thusreaction temperature is normally slowly in creased during the on-streamperiod to maintain constant octane. The maximum reactor inlettemperature, generally about l,O00-1,050F., is set by the onset of rapidcatalyst deactivation. After'the reactants pass through the reactors andreheat furnaces needed to supply reaction heat requirements, theproducts are cooled by heat exchange. The actual number of reactorsemployed in a semi-regenerative operation varies depending upon the feedquality and product octane level desired. Generally, two, three, four orfive reactors are employed.

The refiner has many options in the design and operation of asemi-regenerative unit. Typically, a semiregenerative hydroforming unitis operated and/or designed for either maximum cycle length (on-streamperiod), that is, the period between catalyst regenerations or theperiod between start-up with fresh catalystand the first regeneration,or for maximum throughput (space velocity) to obtain product having agiven octane level. Ordinarily, when operating to secure maximum cyclelength, one employs low severity process conditions to minimize the rateof catalyst deactivation due to deposition of carbonaceous residues onthe catalyst. Thus, to obtain long cycle lengths, the refiner, whenconventional catalysts are used, must sacrifice product yield or productquality by operating at high pressures and/or high hydrogen to naphtharatios, and must employ low space velocities.

According to the present invention, it has been discovered that a veryspecific type of supported platinum/iridium catalyst can be employed ina semiregenerative naphtha reforming process for substantial on-streamperiods at severity conditions beyond the capability of commerciallyavailable platinum and platinum/rhenium catalysts. This unusualperformance capability is illustrated in the FIGURE. In the FIGURE arepresented operating bands A, B and C. These bands encompass the range ofpractical operations which might be employed with each catalyst, basedupon correlated laboratory, pilot plant, literature, and refinery data.As is evident from the FIGURE, at any given severity factor the specificplatinum/iridium catalyst of the present invention (band A) can beemployed in a semi-regenerative reforming operation for an onstreamcycle length considerably longer than those obtainable with aplatinum/rhenium catalyst (band B) or a conventional platinum catalyst(band C).

The catalyst employed in the semi-regenerative reforming process of thepresent invention comprises alumina, preferably eta or gamma alumina ormixtures thereof, in association with 0.15 to 0.75 wt. percent platinum,0.15 to 0.45 wt. percent iridium, and 0.3 to 2.0 wt. percent chlorinepromoter, each based on the total weight of anhydrous catalyst. Ofcourse, other constituents may be present on the catalyst. The surfacearea of the platinum and iridium present on the alumina must bemaintained at a level of at least about 200 square meters per gram (m/gm) of platinum and iridium present, as determined by carbon monoxidechemisorption techniques (see Sinfelt and Yates, J. Catalysis, 8, 82-90(1967)). The catalyst should contain less than about two atoms of sulfurper atom of platinum/iridium present in the catalyst and further besubstantially free of alkali or alkaline earth metal constituents.

The platinum/iridium catalyst can be prepared by impregnating thealumina support material with a solution of a soluble iridium compoundand a soluble platinum compound. Desirably, an aqueous solution of themetal compounds is used. It is essential that the metal compounds beimpregnated on the alumina simultaneously to maximize the desiredinteraction between the iridium and platinum and thus promote theformation of a highly dispersed cluster structure in the final reducedform of the catalyst. The alumina is impregnated with an aqueoussolution of decomposable compounds of iridium and platinum in sufficientconcentration to provide the desired quantity of metal in the finishedcatalyst. Iridium and platinum compounds suitable for incorporation ontothe alumina support material include, among others, chloroiridic acid,iridium tribromide, ammonium chloroiridate, iridium trichloride,chloroplatinic acid, ammonium chloroplatinate, platinum amine salts,etc.

Following the impregnation of the alumina with the iridium and platinumcompounds, the composite catalyst is dried at a temperature varying fromabout 220 to 250F. The catalyst may be dried in air at the above statedtemperatures or may be dried by treating the cat- .alyst in a flowingstream of hydrogen or inert gas. The

drying step may be followed by an additional calcination at atemperature of about 500 700F. Care must be taken to avoid contactingthe catalyst at temperatures in excess of about 800F. with anoxygencontaining gas. Otherwise the iridium will be oxidized, with lossof surface area, to crystallites of iridium oxide, and the polymetalliccluster structure will not be obtained on reduction.

A halogen, particularly chlorine, is a necessary catalyst constituentand is normally present in amounts varying from about 0.3 2.0 wt.percent, preferably 0.6

lyst. The halogen may be incorporated into the total catalyst compositeat any stage in the catalyst manufac- 1.5 wt. percent, based on totaldry weight of the cata- Y ture, i.e., before, during or afterincorporation of the catalyst metals onto the alumina. Halogen is oftenincorporated into the catalyst when impregnating the support withhalogen-bearing catalyst components such as chloroiridic acid andchloroplatinic acid. Further amounts of halogen may be incorporated inthe catalyst by contacting it with chlorine, hydrogen chloride, ammoniumchloride, C C alkyl chlorides, etc., either during catalyst preparationor in subsequent use.

As stated previously, the specific platinum/iridium catalyst is capableof reforming a naphtha feed stock to a high octane product for unusuallylong on-stream periods. More specifically, the instant catalyst systemcan be used in a naphtha reforming process wherein hydrogen and anaphtha feed stock having a Watson characterization factor of from about11.4 to 12.2 are contacted in the presence of the-catalyst at atemperature of less than about 1,050F., preferably from about 750 to1,000F., a pressure of from about 150 to 600 psig, a hydrogen to naphthafeed stock molar ratio (H/O) of from about 2.5:1 to 8:1, and a weighthourly space velocity (pounds of feed stock per hour per pound ofcatalyst (W/H/W)) of from about 0.5 to 6.0 to produce a C reformateproduct having a research octane number (RON), as determined by ASTMtest D269968, of from about 94 to 102. The process is characterized bycarrying out the contacting operation for an onstream period beyond thelimits normally obtainable with a conventional catalyst, specificallywithin the limits of band A of the FIGURE, without incurring a C liquidyield decline of greater than about 3.0 volume percent during saidon-stream period, as determined from a base yield obtained 200 hoursafter the initial contacting of the naphtha feed stock and hydrogen withfresh or freshly regenerated catalyst. Severity factor equals 43.78 0.44(RON) 0.70 In (H/O) 2.0 In W/H/W, and applies to RON variations from 94to 102, I-l/O variations from 2.5:1 to 8:1 and W/H/W variations fromabout 0.5 to 6.0. In a preferred system, the process is carried out atpressures varying from 150 to 400 psig with a catalyst comprising 0.3wt. percent platinum, 0.3 wt. percent iridium, and 0.6 to 1.5 wt.percent chlorine on alumina, the amounts of catalyst components presentbeing based on the total anhydrous weight of the catalyst.

In general, long cycle lengths at relatively high sever-' ity conditionscan be achieved when processing a wide variety of naphtha feed stockswith the catalyst of the present invention. Suitable feeds includesubstantially sulfurfree naphtha streams that typically contain about 15volume percent paraffins, 15 80 volume percent naphthenes, and about 220 volume percent aromatics and that boil at atmospheric pressure attemperatures substantially between about 80 and 450F., preferablybetween about and 375F. In general, any naphtha feed stock having aWatson characterization factor (K of from about 11.4 to 12.2 can beprocessed to high octane C liquid products using the process of thepresent: invention. The Watson characterization factor is a well-knownindex of the chemical character of petroleum fractions. Naphthas havinghigh Watson characterization factors are more difiicult to convert tohigh octane products than naphtha feeds that have lower Watsoncharacterization factors. The

Watson characterization factor of a petroleum fraction is equal to thecube root of the mean average boiling point in degrees Rankine dividedby the specific gravity at 60F. Mean average boiling point is definedas, the boiling point of the petroleum fraction which best correlatesthe molecular weight of the fraction. The mean average boiling point ofa petroleum fraction can be determined by means known to those skilledin the art and is typically obtained, using known correlations, from thevolume average boiling point of the petroleum fraction which in turn isobtained by integrating or averaging the distillation curve of saidfraction (temperature versus liquid volume percent distilled). Furtherinformation regarding the determination of mean average boiling point ofpetroleum fractions can be obtained by reference to Data Book onHydrocarbons, J. B. Maxwell, D. VanNostrand Company, Inc., l950.

As is evident from the FIGURE, the cycle length that may be obtained inan operation to produce high octane C reformate with minimal yield lossis much greater for a platinum/iridium catalyst than for platinum orplatinum-rhenium. This result is true for either a poor quality feed,such as a highly paraffinic material, or an easily reformed feed, suchas a medium boiling naphthenic material. The fact that very long cyclelengths can be obtained is commercially significant since the refinercan operate his process with minimum loss of time for catalystregenerations.

What is claimed is:

l. A naphtha reforming process comprising contacting a naphtha feedstock having a Watson characterization factor of from about ll.4 to 12.2and hydrogen with a catalyst comprising alumina in association with 0.150.75 wt. percent platinum, 0.15 0.45 wt. percent iridium and 0.3 2.0 wt.percent chlorine, each based on total anhydrous catalyst, the surfacearea of said platinum and iridium on said alumina being at least about200 square meters per gram of platinum and iridium, as determined bycarbon monoxide chemisorption techniques, said catalyst containing lessthan about two atoms of sulfur per atom of platinum and iridium andbeing substantially free of alkali and alkaline earth metalconstituents, said contacting being conducted at a temperature of lessthan about l050F. and a pressure of from about ISO to 600 psig. at ahydrogen to naphtha feed stock molar ratio (H/O) of from about 2.5:] to8:1 and a weight hourly space velocity (W/H/W) varying from about 0.5 to6.0: to produce a C reformate product having a research octane numberclear (RON) of from 94 l02. the process being characterized byconducting the contacting for an on-stream period within the limits ofband A of the FIGURE wherein severity factor is determined from theequation, severity factor =43.78+ 0.44 (RUN) 0.70 In (H/O) 2.0 In(W/H/W), and without incurring during said onstream period a C liquidyield decline greater than 3.0 volume percent referred to the C liquidyield obtained 200 hours after the initial contacting of said naphthafeed stock with fresh or regenerated catalyst.

2. The process of claim 1 wherein said naphtha feed stock issubstantially sulfur free.

3. The process of claim 1 wherein said contacting is conducted at apressure varying from about to 400 pslg.

4. The process of claim 1 wherein said contacting is conducted at atemperature in the range of from about 750 to l,000F.

5. The process of claim 1 wherein said catalyst contains from 0.6 to 1.5wt. percent chlorine.

6. The process of claim 1 wherein said catalyst contains about 0.3 wt.percent platinum, 0.3 wt. percent iridium and about 0.6 to 1.5 wt.percent chlorine.

7. The process of claim 6 wherein said contacting is conducted at apressure varying from about 150 to 400 psig.

- 8. The process of claim 7 wherein said contacting is conducted at atemperature in the range of from about 750F. to l,000F.

1. A NAPHTHA REFORMING PROCESS COMPRISING CONTACTING A NAPHTHA FEED STOCK HAVING A WATSON CHARACTERIZATION FACTOR OF FROM ABOUT 11.4 TO 12.2 AND HYDROGEN WITH A CATALYST COMPRISING ALUMINA IN ASSOCIATION WITH 0.15-0.75 WT. PERCENT PLATINUM, 0.15-0.45 WT. PERCENT IRIDIUN AND 0.3-2.0 WT. PERCENT CHLORIDE, EACH BASED ON TOTAL ANHYDROUS CATALYST THE SURFACE AREA OF SAID PLATINUM AND IRIDIUM ON SAID ALUMINA BEING AT LEAST ABOUT 200 SQUARE METERS PER GRAM OF PLATINUM AND IRIDIUM, AS DETERMINED BY CARBON MONOXIDE CHEMISORPTION TECHNIQUES, SAID CATALYST CONTAINING LESS THAN ABOUT TWO ATOM OF SULFUR PER ATOM OF PLATINUM AND IRIDIUM AND BEING SUBSTANTIALLY FREE OF ALKALI AND ALKALINE EARTH METAL CONSTITUENTS, SAID CONTACTING BEING CONDUCTED AT A TEMPERATURE OF LESS THAN ABOUT 1050*F AND A PRESSURE OF FROM ABOUT 150 TO 600 PSIG. AT A HYDROGEN TO NAPHTHA FEED STOCK MOLAR RATIO (H/O) OF FROM ABOUT 2.5:1 TO 8:1 AND A WEIGHT HOURLY SPACE VELOCITY (W/H/W) VARYING FROM ABOUT 0.5 TO 6.0 TO PRODUCE A C5+ REFORMATE PRODUCT HAVING A RESEARCH OCTANE NUMBER CLEAR (RON) OF FROM 94 TO-102, THE PROCESS BEING CHARACTERIZED BY CONDUCTING THE CONTACTING FOR AN ON-STREAM PERIOD WITHIN THE LIMITS OF BAND A OF THE FIGURE WHEREIN SEVERITY FACTOR=-43.78+0.4 DETERMINED FROM THE EQUATION, SEVERITY FACTOR=-43.78+44 (RON)-0.70 IN (H/O) + 2.0 IN (W/h/W), AND WITHOUT INCURRING DURING SAID ON-STREAM PERIOD OF C5+ LIQUID YEILD DECLINE GREATER THAN 3.0 VOLUME PERCENT REFERRED TO THE C5+ LIQUID YEILD OBTAINED 200 HOURS AFTER THE INITIAL CONTACTING OF SAID MAPHTHA FEED STOCK WITH FRESH OR REGENERATED CATALYST.
 2. The process of claim 1 wherein said naphtha feed stock is substantially sulfur free.
 3. The process of claim 1 wherein said contacting is conducted at a pressure varying from about 150 to 400 psig.
 4. The process of claim 1 wherein said contacting is conducted at a temperature in the range of from about 750* to 1,000*F.
 5. The process of claim 1 wherein said catalyst contains from 0.6 to 1.5 wt. percent chlorine.
 6. The process of claim 1 wherein said catalyst contains about 0.3 wt. percent platinum, 0.3 wt. percent iridium and about 0.6 to 1.5 wt. percent chlorine.
 7. The process of claim 6 wherein said contacting is conducted at a pressure varying from about 150 to 400 psig.
 8. The process of claim 7 wherein said contacting is conducted at a temperature in the range of from about 750*F. to 1,000*F. 